NOx Adsorber Desulfation Techniques for Heavy-Duty On-Highway Diesel Engines

A 5.9 liter medium-heavy-duty diesel engine, equipped with a diesel exhaust emission control system consisting of catalyzed diesel particulate filters (CDPF) and NOx adsorber catalysts arranged in a dual-path configuration, was evaluated with the goal of developing desulfation strategies for in-use NOx adsorber desulfation. NOx adsorber desulfation was accomplished by providing reductant via a secondary exhaust fuel injection system and exhaust flow via an exhaust bypass valve. An alternating restriction of the exhaust flow between the two flow paths allowed reductant injection and adsorber desulfation to occur under very low space velocity conditions. An exhaust bypass valve connecting the dual path configuration upstream of the catalyzed diesel particulate filters allowed controlled addition of exhaust into the desulfating pathway for desulfation method development. Exotherms from the oxidation of reductant on the CDPF, and subsequent convective heat transfer from the CDPF to the NOx adsorbers generated adsorber catalyst temperatures in excess of 750°C. The control of space velocity through the desulfating pathway minimized cooling, allowing the temperature to be held in the target desulfation temperature range for prolonged periods of time. Sulfur release in the form of hydrogen sulfide and sulfur dioxide was measured using a chemical ionization mass spectrometer.